1. Field of the Invention
The present invention relates to a photovoltaic device, more particularly, to a photovoltaic device provided with a transparent conductive oxide film and a collector electrode on the transparent conductive oxide film and having greater environmental durability and reliability.
2. Description of the Related Art
Since solar power generation systems mounted on a roof has become widespread rapidly, solar cells with greater environmental durability and environmental reliability than that of conventional home-use solar cells are required recently. Generally, the structures of solar cell modules are designed so as to obtain sufficient environmental durability, but more preferably, photoelectric conversion elements in the solar cell modules should possess excellent environmental durability and reliability. In a photovoltaic device using a comb-shaped metal electrode and a transparent conductive oxide film comprised of indium tin oxide (Sn-doped In2O3: ITO) or zinc oxide (ZnO) on the light incident side, for example, high reliability in moisture resistance and alkaline resistance is required to not only semiconductor layers but also the transparent conductive oxide film.
A highly effective transparent conductive oxide film needs high light-transmittance and low electric resistance together. Generally, a high crystallinity is necessary for transparent conductive film to obtain the high light-transmittance and the low electric resistance. However, because ITO films and ZnO films are polycrystals, their grain boundaries are affected with an increase in size of their crystal grains. That is, the grain boundaries work as a path to accelerate alkaline to leach out from glass, thereby causing a possible decrease in the environment durability and reliability.
In order to solve the problem, a method of laminating two kinds of ITO films each having different crystal orientation has been proposed to realize high reliability. (e.g. Japanese unexamined patent publication No. 2003-347571). Also, photoelectric conversion device in which after forming photovoltaic elements, a light incident side of the elements is covered with a resin moist-proof film has been proposed (e.g. Japanese unexamined patent publication No. 1998-107308).
The photovoltaic devices disclosed in the above-mentioned publications achieve the high reliability, but no description has been made on adhesion property of collector electrodes therein. Further improvement of the adhesion property is necessary.